The present disclosure relates to electronic circuits and methods, and in particular, to envelope tracking circuits and methods with adaptive switching frequency.
Envelope Tracking (ET) is a technique aimed at boosting the efficiency of a power amplifier (PA) by continuously adjusting its power supply voltage according to a signal envelope to improve efficiency during transmission. FIG. 1 shows an example configuration for one type of envelope tracking system. In this example, an input signal Vin is provided at the input of a power amplifier (PA) 103 to produce a power amplified signal Vout. PA 103 receives a power supply voltage Vdd and a power supply current Idd from a configuration of a linear amplifier 101 and a switching stage 102. The linear and switching stages work together to adjust the level of Vdd based on the envelope of Vin so that PA 103 operates in a more efficiency region of operation. In this example, linear amplifier 101 receives an envelope tracking signal (ET) representing the envelope of Vin, for example. Linear amplifier 101 may produce a voltage Vdd and current Iamp. Switching stage 102 receives a switching signal SW based on the envelope signal. In this example, SW is generated by sensing Iamp. Switching stage 102 produces a voltage Vdd and current Isw. The sum of currents Iamp and Isw are the power supply current Idd drawn by PA 103. The switching regulator stage 102 boosts the ET's efficiency but it is noisy. The linear regulator stage 101 is higher speed and ensures the optimum power supply voltage to achieve the PA's peak efficiency, but it is (power) lossy. Unfortunately, the noise and efficiency are the contradictory performance requirements.
Obtaining power-efficiency and noise performance across a wide bandwidth range of an envelope waveform is a challenge for conventional envelope tracking amplifiers.